Laser-Induced Graphene Supercapacitors by Direct Laser Writing of Cork Natural Substrates

Interdigitated and square laser-induced graphene (LIG) electrodes were successfully fabricated by direct laser writing of common natural cork bottle stoppers. The laser graphitization process was performed with a low-cost hobbyist visible laser in a simple, fast, and one-step process under ambient conditions. The formation of LIG material was revealed by extensive characterization using Raman, attenuated total reflection-Fourier transform infrared (ATR-FTIR), and X-ray photoelectron (XPS) spectroscopies. Electron microscopy investigation showed that the formed LIG structure maintained the hierarchical alveolar structure of the pristine cork but displayed increased surface area, disorder, and electrical conductivity, promising for electrochemical applications. Open planar and sandwich supercapacitors, assembled from fabricated electrodes using poly(vinyl alcohol) PVA/H+ as an electrolyte, exhibited a maximum areal capacitance of 1.56 mF/cm2 and 3.77 mF/cm2 at a current density 0.1 mA/cm2, respectively. Upon treatment with boric acid (H3BO3), the areal capacitance of the resulting boron-doped LIG devices increased by ca. three times, reaching 4.67 mF/cm2 and 11.24 mF/cm2 at 0.1 mA/cm2 current density for planar and sandwich configurations, respectively. Supercapacitor devices showed excellent stability over time with only a 14% loss after >10 000 charge/discharge cycles. The easy, fast, scalable, and energy-efficient method of fabrication illustrated in this work, combined with the use of natural and abundant materials, opens avenues for future large-scale production of "green" supercapacitor devices.